The availability of a capillary bed in close proximity to the implanted cells, in an exemplary case islet cell clusters, is disclosed as promoting engraftment of the cellular transplant. Furthermore the presence of the co-transplanted sertoli cells is thought to confer immunoprotection/immunomodulation within the device. Sertoli cells are derived from the testis and express FasL (Fas ligand). These cells are thought to be able to confer local immunoprotection and in the case of the testis microenvironment, allow for prolonged survival of other cell types transplanted into the testis. Intratesticulat transplantation of cells such as islets, or co-transplantation of islets with sertoli cells has been attempted for the past two decades, with the objective to confer immunoprotection from the immune-attack of the transplanted cells by the recipient immune system.